The invention discloses an automatic insulator flaw detection instrument and method, which can realize on-line real-time detection without outage, ensure the result accuracy and improve the detection accuracy. The automatic insulator flaw detection instrument comprises an ultrasonic receiving module, a signal conditioning unit and an analog/digital conversion unit which are sequentially connected with one another, an infrared core and a digital receiving module which are sequentially connected with each other, a signal processing module connected to the output ends of the analog/digital conversion unit and the digital receiving module, a data storage unit, a SD storage card and a keyboard which are connected with the signal processing module, a fault alarm unit and a display unit which are connected to the output end of the signal processing module, and a power supply module which supplies power to the ultrasonic receiving module, the signal processing module, the signal conditioning unit and the data storage unit. Whether an ultrasonic signal is transmitted from an insulator part is detected by the ultrasonic receiving module, the insulator is subjected to imaging processing by an infrared imaging technology, and whether the thermal field change on the surface of the insulator is abnormal is detected, so that whether the insulator has a fault and the fault position are judged.